Transformer Differential Protection is a system used to protect transformers from electrical faults. It works by monitoring the current difference between the transformer’s primary and secondary sides and comparing it to a predetermined threshold. If the difference exceeds the point, it indicates a fault in the transformer, and the protection system will trip the circuit breaker to disconnect the transformer from the power grid.
Failures can also happen inside the transformer, such as short circuits in the windings, between the turns, between the phases, in the core, in the transformer tanks, or on the bushing. When it comes to where a failure might happen, the protection systems for transformers can be split into two groups: external and internal. The main job of a protective device is to disconnect the transformer from of the energy source as soon as possible. This keeps bad things from happening and keeps the transformer from getting seriously damaged. The protection is set up to send a signal if there are problems with the electrical system that could cause the transformer to break.
Differential protection (I) is the most essential and widely used type of transformer protection. It is safe and reliable. It protects transformers with a rated power of more than 8 MVA. It isn’t usually used with transformers with a nominal capacity of less than 4 MVA.
Possible measures cover almost all shunts inside the transformer, including those between phases, between turns, and between step and ground. If the neutral of the transformer is directly connected to the ground, this protection also covers insulation breakdown in all of the windings. If the neutral of the transformer is cut off, the differential protection will only cover problems between two phases, not issues with just one phase.
There are several advantages to using differential protection for transformers:
- High accuracy: Differential protection is highly accurate and can detect slight differences in current, which allows it to detect faults quickly and reliably.
- Fast response: Differential protection can respond quickly to fault conditions, typically within a few milliseconds, which helps to minimize damage to the transformer and other equipment.
- Sensitivity to internal faults: Differential protection is particularly effective at detecting internal defects within the transformer, such as short circuits or phase-to-ground marks, which can be challenging to see using other protection methods.
- Immunity to external influences: Differential protection is immune to external forces such as harmonics and transients, which can interfere with other protection methods.
Differential protection is typically used in conjunction with other protection systems to provide comprehensive protection for transformers. It is an integral part of the electrical power grid and helps to ensure the reliable and stable operation of transformers.
How to Find Threshold Differential Protection Current
The threshold differential protection current for a transformer is the maximum difference in current between the primary and secondary sides of the transformer that is allowed before the protection system trips the circuit breaker to disconnect the transformer from the power grid.
Several factors can influence the threshold differential protection current for a transformer, including:
The type of fault: Different threshold values may be used for different kinds of spots, such as phase-to-phase or phase-to-ground faults.
The size of the transformer: Larger transformers may require higher threshold values due to the increased current flow.
The design of the protection system: Different protection systems may have different threshold values depending on their design and the type of sensors or relays they use.
To determine a transformer’s threshold differential protection current, it is necessary to consider these factors and refer to the manufacturer’s specifications or industry standards.
Setting the corresponding limit differential protection current is a challenging task. It ought to be low enough that a faulty draft can be found quickly and a transformer taken out of service. On the other side, it must be high enough to avoid wrong procedure in some normal transformer conditions. Such as when the transformer is first turned on (when the current is higher) or when there is no load (when the current is DC).